make the cake layers
Preheat the oven to 350 degrees. Line three 8-inch round cake pans with parchment paper. Butter pans and dust with cocoa powder (instead of flour which leaves white splotches on the chocolate layers), shaking off the excess.
In a double boiler, melt dark chocolate. Remove from heat and cool. Quicken this step by cooling chocolate in the refrigerator.
In a medium bowl, sift the cake flour, cocoa powder, baking powder, baking soda and salt. In a small bowl or large measuring cup, whisk together coffee and buttermilk.
In a mixer fitted with the paddle attachment, beat butter and sugar together until fluffy, about three minutes. Add eggs, one at a time, scraping sides of bowl down after each addition. Add vanilla and mix until incorporated. Add the flour mixture in three additions, alternating with the coffee/buttermilk mixture. Begin and end with the flour mixture. Remove the bowl from the mixer and using a spatula, fold in the melted chocolate.
Divide the batter evenly between the three pans. Batter should fill pans about half to two-thirds of the way full. Smooth the tops with a spatula. Bake for 30 to 35 minutes, or until a toothpick inserted in the middle comes out clean. Transfer cakes to a wire cooling rack for 20-30 minutes. Invert cakes onto rack and remove pans and parchment to let cool completely.
make the filling
In a large saucepan, whisk together egg yolks, evaporated milk and vanilla until well blended. Add sugars and butter and cook over medium heat, stirring often, for 12 minutes, until mixture is thickened. Remove from heat. Mix in coconut and pecans. Cool to room temperature.
assemble the cake
Trim tops of cakes to level out surface, if necessary. Place first cake layer on platter or cake stand. Spread one third of filling on top. Add second layer and spread another third of filling on top. Follow with final layer and top with remaining filling.